Data Storage Object Cloning in a Multi-Appliance Federation

1. A method of creating a clone, on a second data storage appliance of a federation, of a source storage object stored on a first data storage appliance of the federation, comprising: at the first data storage appliance, creating a snapshot being a point-in-time copy of the source storage object; performing a full copy of the snapshot from the first data storage appliance to the second data storage appliance to produce a copy snapshot on the second data storage appliance; at the second data storage appliance, creating the clone from the copy snapshot and incorporating the clone into a federation-wide family association of the source storage object; and subsequently: 1. Having separate applications access the clone and the source storage object at the first and second data storage appliances respectively, and 2. Maintaining the clone in synchronism with the source storage object by subsequent refresh operations each including (i) creating a new snapshot of the source storage object on the first data storage appliance, (ii) copying a snapshot difference between the new snapshot and the snapshot on the first data storage appliance to the second data storage appliance, the snapshot difference being used to create a new copy snapshot referenced to the copy snapshot on the second data storage appliance, the new copy snapshot containing volume state from which the clone can be refreshed, (iii) and refreshing the clone from the new copy snapshot.

2. The method of claim 1, wherein block sharing is used within the first data storage appliance and the second data storage appliance to realize the snapshot and the clone respectively, and the full copy is necessitated by lack of block sharing between the first and data storage appliances.

3. The method according to claim 1, wherein the source storage object is a primary volume having a highest position in a tree-structured representation of the family association.

4. The method according to claim 1, wherein the clone is a new clone and the source storage object is an existing clone of a primary volume, the existing clone having an intermediate position in a tree-structured representation of the family association.

5. The method according to claim 4, wherein the snapshot is subsequently retained at the first data storage appliance.

6. The method according to claim 4, applied recursively to migrate a clone tree having a plurality of clones in the family association.

7. The method of claim 1, wherein the snapshot is a first snapshot and the copy snapshot is a first copy snapshot, and further including refreshing the source storage object from the clone by steps including: creating a second new snapshot of the clone on the second data storage appliance; copying a snapshot difference between the second new snapshot and the first copy snapshot on the second data storage appliance to the first data storage appliance, the snapshot difference being used to create a second new copy snapshot referenced to the first snapshot on the first data storage appliance, the second new copy snapshot containing volume state from which the source storage object can be refreshed; and refreshing the source storage object from the second new snapshot copy.

8. The method of claim 7, wherein the source storage object is a primary volume.

9. A data storage system including front-end interface circuitry for interfacing to separate client computers, physical storage devices providing physical data storage, processing circuitry, and back-end interface circuitry for interfacing to the physical storage devices, the processing circuitry including one or more processors and memory for storing and executing computer software to cause the data storage system to function as a first data storage appliance of a multi-appliance federation by co-operating with a second data storage appliance of the federation to create a clone on the second data storage appliance of a source storage object stored on the first data storage appliance, by: creating a snapshot being a point-in-time copy of the source storage object; performing a full copy of the snapshot from the first data storage appliance to the second data storage appliance to produce a copy snapshot on the second data storage appliance; upon creation of the clone from the copy snapshot at the second data storage appliance, incorporating the clone into a federation-wide family association of the source storage object; and subsequently: 1. Having separate applications access the clone and the source storage object at the first and second data storage appliances respectively, and 2. Maintaining the clone in synchronism with the source storage object by subsequent refresh operations each including (i) creating a new snapshot of the source storage object on the first data storage appliance, (ii) copying a snapshot difference between the new snapshot and the snapshot on the first data storage appliance to the second data storage appliance, the snapshot difference being used to create a new copy snapshot referenced to the copy snapshot on the second data storage appliance, the new copy snapshot containing volume state from which the clone can be refreshed, (iii) and refreshing the clone from the new copy snapshot.

10. The data storage system of claim 9, wherein block sharing is used within the first data storage appliance and the second data storage appliance to realize the snapshot and the clone respectively, and the full copy is necessitated by lack of block sharing between the first and data storage appliances.

11. The data storage system of claim 9, wherein the source storage object is a primary volume having a highest position in a tree-structured representation of the family association.

12. The data storage system of claim 9, wherein the clone is a new clone and the source storage object is an existing clone of a primary volume, the existing clone having an intermediate position in a tree-structured representation of the family association.

13. The data storage system of claim 12, wherein the snapshot is subsequently retained at the first data storage appliance.

14. The data storage system of claim 12, wherein recursive operation is used to migrate a clone tree having a plurality of clones in the family association.

15. The data storage system of claim 9, wherein the snapshot is a first snapshot and the copy snapshot is a first copy snapshot, and wherein operation further includes refreshing the source storage object from the clone by steps including: creating a second new snapshot of the clone on the second data storage appliance; copying a snapshot difference between the second new snapshot and the first copy snapshot on the second data storage appliance to the first data storage appliance, the snapshot difference being used to create a second new copy snapshot referenced to the first snapshot on the first data storage appliance, the second new copy snapshot containing volume state from which the source storage object can be refreshed; and refreshing the source storage object from the second new snapshot copy.

16. The data storage system of claim 15, wherein the source storage object is a primary volume.